The present invention relates to dielectric resonator devices, dielectric filters and dielectric duplexers for use in communications devices, image devices, etc.
Mobile communications systems using a frequency band of hundreds of megahertz to several gigahertz have terminal devices comprising a receiving circuit 52 and a transmitting circuit 62 which are connected in parallel with an antenna 7 via a duplexer 72 to use the single antenna 7 for both the receiving circuit 52 and the transmitting circuit 62 as shown in FIG. 35. The duplexer 72 comprises a receiving filter 50 and a transmitting filter 60, each of which is provided, for example, by a coaxial dielectric resonator 20 shown in FIG. 38.
With reference to FIG. 38, the coaxial dielectric resonator 20 comprises a rectangular parallelepipedal dielectric block 21 having a bore 22 extending therethrough, an outer conductor layer 24 and an inner conductor layer 23 which are formed on the dielectric block 21 respectively over the outer peripheral surface thereof and the inner peripheral surface thereof defining the bore 22, and a short-circuiting conductor layer 25 formed on the dielectric block 21 over an end face thereof where the bore 22 has an opening and providing a short circuit between the outer conductor layer 24 and the inner conductor layer 23.
With reference to FIG. 39(a) showing the coaxial dielectric resonator 20, the outer conductor layer 24 is connected to the ground, and the inner conductor layer 23 to a signal input terminal S, whereby the coaxial dielectric resonator 20 is made equivalent to a circuit comprising an inductance element and a capacitance element which are connected in parallel with each other as shown in FIG. 39(b), thus providing a trap filter having a resonance frequency which is determined by the inductance of the inductance element L and the capacitance of the capacitance element C.
Terminal devices which are usable for a plurality of communications systems of different frequency bands are required of mobile communications systems. Accordingly, it has been proposed to use a dielectric resonator device shown in FIG. 37 (see, for example, JP-A No. 7-147503/1995) for the receiving filter 50 and transmitting filter 60.
The dielectric resonator device is provided by connecting a switch SW to the point of connection between the inner conductor layer 23 of the coaxial dielectric resonator 20 and the signal input terminal S, via an external capacitor element C0, such that the capacitance C0 of the external capacitor element can be connected to or disconnected from a capacitance C provided between the outer conductor layer 24 of the resonator 20 and the inner conductor layer 23 thereof by operating the switch SW. The resonance frequency of the resonator 20 alters with the variation of capacity effected by switching.
FIG. 36 shows an arrangement of a receiving filter 50 and a transmitting filter 60 each comprising such a dielectric resonator device. As illustrated, the receiving filter 50 has a signal line extending from a receiving connection terminal 51 to an antenna terminal 71, and a plurality of capacitance elements C4, C5 and C6 provided on the signal line. The transmitting filter 60 has a signal line extending from a transmitting connection terminal 61 to the antenna terminal 71, and a plurality of capacitance elements C4xe2x80x2, C5xe2x80x2 and C6xe2x80x2 provided on the signal line. Two coaxial dielectric resonators 20, 20 are connected to each of the signal lines. A switch SW is connected via a capacitance element C0 to the point of connection between each resonator 20 and the signal line. Accordingly, the pass bands of the receiving filter 50 and the transmitting filter 60 can be altered for a changeover between two kinds of receiving/transmitting frequencies by operating these switches SW.
It has been demanded in recent years that mobile communications terminal devices, such as portable telephones, be made ever smaller in size, giving rise to the great problem of how to reduce the number of electric or electronic components and how to diminish the sizes of such components. However, the dielectric resonator device shown in FIG. 37 has the problem that the need to connect the external capacitor C0 in the form of a chip to the coaxial dielectric resonator 20 increases the number of components of the device and makes the device large-sized. Further since chip capacitors are great in capacity tolerance, the capacitor requires an additional circuit (not shown) for finely adjusting the capacity, hence a further increase in the number of components.
An object of the present invention is to provide a dielectric resonator device having a resonance frequency which is accurately variable without necessitating an external capacitor, and a dielectric filter and a dielectric duplexer which comprise the resonator device.
The present invention provides a dielectric resonator device comprising a coaxial dielectric resonator 2 which comprises a dielectric block 21 having a bore 22 extending therethrough, an outer conductor layer 24 formed on an outer peripheral surface of the dielectric block 21, an inner conductor layer 23 formed on the dielectric block 21 over an inner peripheral surface thereof defining the bore 22, a short-circuiting conductor layer 25 formed on the dielectric block 21 over an end face thereof where the bore 22 has an opening and providing a short circuit between the outer conductor layer 24 and the inner conductor layer 23, and a separated conductor layer 3 formed on the outer peripheral surface of the dielectric block 21 and electrically separated from the outer conductor layer 24.
The separated conductor layer 3 of the resonator 2 has connected thereto a switch SW by which the capacitance Cxe2x80x2 provided between the separated conductor layer 3 and the inner conductor layer 23 is connected to or disconnected from the capacitance C provided between the outer conductor layer 24 and the inner conductor layer 23 upon switching to thereby vary the resonance frequency of the resonator 2.
With the dielectric resonator device of the invention, the inner conductor layer 3 of the resonator 2 is connected, for example, to a signal input terminal S, and the outer conductor layer 24 is connected to the ground.
With the device described above, the separated conductor layer 3 on the outer peripheral surface of the dielectric block 21 of the resonator 2 is opposed to the inner conductor layer 23, providing a capacitance Cxe2x80x2 between the two layers. The capacitance Cxe2x80x2 is connected to or disconnected from the capacitance C between the outer conductor layer 24 and the inner conductor layer 23 by operating the switch SW, thus performing the same function as a conventional external capacitor.
Stated more specifically, the separated conductor layer 3 of the resonator 2 is connected to the ground via the switch SW. Accordingly, when closed, the switch SW connects the separated conductor layer 3 to the ground, whereby the capacitance Cxe2x80x2 between the separated conductor layer 3 and the inner conductor layer 23 is connected to the capacitance C between the outer conductor layer 24 and the inner conductor layer 23 to shift the resonance frequency of the resonator 2 toward the lower frequency side. Alternatively when opened, the switch SW cuts off the separated conductor layer 3 from the ground, with the result that the capacitance Cxe2x80x2 between the separated conductor layer 3 and the inner conductor layer 23 becomes no longer involved in the resonance frequency of the resonator 2 to shift the resonance frequency toward the higher frequency side.
Further stated more specifically, the separated conductor layer 3 of the resonator 2 is provided by forming a groove 26 in the outer conductor layer 24 covering the outer peripheral surface of the dielectric block 21 and separating off a portion of the outer conductor layer 24. The groove 26 can be formed, for example, by ultrasonic machining. The resonance frequency of the resonator 20 can be made to match the designed value with high accuracy by finely adjusting the area of the separated conductor layer 3 during machining of the groove 26.
Further stated more specifically, the separated conductor layer 3 comprises a first separated conductor layer 31 and a second separated conductor layer 32 which are electrically separated from each other, the first separated conductor layer 31 being connected to an input signal terminal S, the second separated conductor layer 32 being connected to the ground via the switch SW, the outer conductor layer 24 being connected to the ground. With this specific construction, a capacitance Cxe2x80x2 is provided between the second separated conductor layer 32 and the inner conductor layer 23, and a capacitance Cxe2x80x3 is provided between the first separated conductor layer 31 and the inner conductor layer 23. Accordingly, when a high-frequency signal to be input to the inner conductor layer 23 is input to the first separated conductor layer 31, the input signal is input to the inner conductor layer 23 through the capacitance Cxe2x80x3. As a result, the wire for feeding the input signal to the inner conductor layer 23 can be dispensed with.
The present invention provides a dielectric filter comprising a first dielectric resonator device 11 and a second dielectric resonator device 12 which are connected to, and located respectively at two positions on, a signal line extending from an input terminal 42 to an output terminal 43, at least one of the dielectric resonator devices comprising the coaxial dielectric resonator 2 of the invention described. The separated conductor layer 3 of the resonator 2 has connected thereto a switch SW by which the capacitance Cxe2x80x2 provided between the separated conductor layer 3 and the inner conductor layer 23 is connected to or disconnected from the capacitance C provided between the outer conductor layer 24 and the inner conductor layer 23 upon switching to thereby give altered signal passage characteristics.
The present invention provides a dielectric duplexer comprising a receiving filter 5 and a transmitting filter 6 which are connected in parallel with an antenna terminal 71 for connecting an antenna 7 thereto, each of the receiving filter 5 and the transmitting filter 6 comprising the coaxial dielectric resonators of the invention described. The separated conductor layer 3 of the resonator 2 has connected thereto a switch SW by which the capacitance Cxe2x80x2 provided between the separated conductor layer 3 and the inner conductor layer 23 is connected to or disconnected from the capacitance C provided between the outer conductor layer 24 and the inner conductor layer 23 upon switching to thereby alter the signal passage characteristics of the receiving filter 5 or the transmitting filter 6.
The present invention provides another dielectric duplexer comprising a receiving filter 54 and a transmitting filter 64 which are connected in parallel with an antenna terminal 71 for connecting an antenna 7 thereto, the receiving filter 54 comprising a main filter circuit 82 having a pass band in the frequency band of the signal to be received and a trap circuit 83 connected in series with the main filter circuit 82 for attenuating the frequency band of the signal to be transmitted, the trap circuit 83 comprising the coaxial dielectric resonator 2 of the invention described. The separated conductor layer 3 of the resonator 2 has connected thereto a switch SW by which the capacitance Cxe2x80x2 provided between the separated conductor layer 3 and the inner conductor layer 23 is connected to or disconnected from the capacitance C provided between the outer conductor layer 24 and the inner conductor layer 23 upon switching to thereby alter the signal passage characteristics of the receiving filter 54.
With the dielectric resonator device, the dielectric filter and the dielectric duplexer according to the invention, the coaxial dielectric resonator 2 itself is provided with a capacitance for varying the resonance frequency as described above, so that the resonance frequency can be altered without necessitating an external capacitor. Further the coaxial dielectric resonator 2 can be set at a designed resonance frequency with high accuracy by finely adjusting the area of the separated conductor layer 3.